# std::fsetpos

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< cpp‎ | io‎ | c

Defined in header `<cstdio>` |  |
int fsetpos( std::FILE* stream, const std::fpos_t* pos ); |  |

Sets the file position indicator and the multibyte parsing state (if any) for the C file stream `stream` according to the value pointed to by `pos`.

Besides establishing new parse state and position, a call to this function undoes the effects of std::ungetc and clears the end-of-file state, if it is set.

If a read or write error occurs, the error indicator (std::ferror) for the stream is set.

### Parameters

stream | - | file stream to modify
pos | - | pointer to a fpos_t object obtained from std::fgetpos called on a stream associated with the same file

### Return value

​0​ upon success, nonzero value otherwise. Also, sets errno on failure.

### Notes

After seeking to a non-end position in a wide stream, the next call to any output function may render the remainder of the file undefined, e.g. by outputting a multibyte sequence of a different length.

### Example

Run this code

    #include <cstdio>
    #include <cstdlib>

    int main()
    {
        // Prepare an array of floating-point values.
        const int SIZE = 5;
        double A[SIZE] = {1., 2., 3., 4., 5.};
        // Write array to a file.
        std::FILE * fp = std::fopen("test.bin", "wb");
        std::fwrite(A, sizeof(double), SIZE, fp);
        std::fclose(fp);

        // Read the values into array B.
        double B[SIZE];
        fp = std::fopen("test.bin", "rb");
        std::fpos_t pos;
        if (std::fgetpos(fp, &pos) != 0)      // current position: start of file
        {
           std::perror("fgetpos()");
           std::fprintf(stderr, "fgetpos() failed in file %s at line # %d\n",
                        __FILE__, __LINE__-3);
           std::exit(EXIT_FAILURE);
        }

        int ret_code = std::fread(B, sizeof(double), 1, fp);      // read one value
        // current position: after reading one value
        std::printf("%.1f; read count = %d\n", B[0], ret_code);   // print one value and ret_code

        if (std::fsetpos(fp, &pos) != 0)   // reset current position to start of file
        {
           if (std::ferror(fp))
           {
              std::perror("fsetpos()");
              std::fprintf(stderr, "fsetpos() failed in file %s at line # %d\n",
                           __FILE__, __LINE__-5);
              std::exit(EXIT_FAILURE);
           }
        }

        ret_code = std::fread(B, sizeof(double), 1, fp);         // re-read first value
        std::printf("%.1f; read count = %d\n", B[0], ret_code);  // print one value and ret_code
        std::fclose(fp);

        return EXIT_SUCCESS;
    }

Output:

    1.0; read count = 1
    1.0; read count = 1

### See also

fgetpos | gets the file position indicator (function)
ftell | returns the current file position indicator (function)
fseek | moves the file position indicator to a specific location in a file (function)
C documentation for fsetpos

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